1. Technical Field
This invention relates to a method for electrochemically processing articles, such as cylindrically shaped, hollow tubing articles, and more specifically, to methods and to apparatuses used for plating processes.
2. Description of the Related Art
One example of hollow articles requiring plating is tubing used in the aerospace field. The tubing is used for flowing fuel, lubricating fluid, hydraulic fluid and the like, typically in high-pressure applications. The tubing is relatively small in diameter (less than one inch) and is typically joined to a mating component using braze material. The tubing frequently receives a coating to provide a smooth surface. The coating is carefully applied because the coated tubing has controlled tolerances. The smooth surface and controlled tolerances ensure that capillary forces will urge the braze material to flow into a predetermined gap between the tubing and the component.
One approach for providing the coating uses a plating process having a large-scale bath and includes disposing many pieces of tubing in the bath. A large-scale plating bath may not efficiently use the plating solutions, increasing purchasing costs and increasing disposal costs of the environmentally sensitive waste. Depending on the location of the tubing in the bath, the tubing might receive a thicker than desired coating or a thinner than desired coating. In addition, a large-scale plating bath may well be located at a site remote from the location at which the brazing processes are carried out.
Another approach for providing the coating is a brush plating process. The electrolytes used for brush plating have a higher metal content than electrolytes for conventional plating baths. Brush plating processes employ a carbon anode wrapped in a conductive pad. The conductive pad is soaked in the electrolyte. This is essential to achieve higher rates of plating deposition. A current is passed through the pad and to the article as the operator rubs the pad over the surface.
An advantage of the brush plating process is little waste and acceptable levels of time for work in process. However, the process is labor-intensive and variations in technique from operator to operator increase the difficulty of precisely controlling the plating thickness. In addition, the operator must handle harsh chemicals during cleaning and etching and must hold and move the anode with a repetitive motion that causes fatigue and which might cause repetitive motion injuries.
Accordingly, scientists and engineers working under the direction of Applicants Assignee have sought to develop a plating process and apparatus for use with such processes that provide efficient use of solutions, efficient use of rinsing water and may be installed in local work areas.
This invention is predicated in part on the recognition that using concentrated solutions of the type having higher metal content for use with high-speed plating may advantageously be used in local work areas by using dedicated plating cells. It is also predicated on recognizing that dedicated cells may be provided with flow patterns that promote rinsing processes and electrochemical processes associated with plating. In this context, electrochemical processes refer to process steps for an article, such as etching, activating and electroplating and other steps that pass a current through an electrolyte. The current is passed between a pair of electrodes where the article acts as one of the electrodes, whether as an anode or a cathode. Rinsing refers to those steps using an apparatus to prepare the surface by removing contaminants from the surface with a rinse fluid, such as by removing electrolyte from the surface with rinse water.
According to the present invention, an electrochemical cell for performing an electrochemical process includes a first electrode having an electrode chamber for receiving electrolyte and an article which forms the second electrode and which is disposed inwardly of the first electrode and spaced from the first electrode leaving a passage for electrolyte therebetween. In accordance with the present invention, the electrolyte passage is in flow communication with a source of electrolyte to flow electrolyte to the electrolyte passage during the electrochemical process.
In accordance with one detailed embodiment of the present invention, means for swirling the electrolyte is disposed in the electrochemical cell for imparting a lateral or circumferential velocity to the electrolyte as the flow passes to electrolyte passage.
In accordance with one detailed embodiment, the electrochemical cell has a guide member for guiding the article as the article is inserted into the electrochemical cell.
In accordance with one embodiment, the guide member is disposed within the electrode chamber and the article extends about the guide member. According to another embodiment, the first electrode extends circumferentially about an axis A to form a circumferentially extending chamber and the second electrode (the article) is a circumferentially extending object which is spaced from the first electrode leaving an annular electrolyte passage therebetween.
According to the present invention, a method of electrochemically treating an article using a pair of electrodes includes: disposing a first electrode about the article to form at least a portion of the chamber for receiving an electrolyte; disposing electrolyte in the chamber; disposing the article in the electrode chamber to form the second electrode and placing the second electrode in electrical communication with the first electrode; and, passing electrical current between the electrodes to electrochemically affect a surface of the article.
In accordance with one embodiment of the present invention, the method includes flowing additional electrolyte into the electrode chamber and displacing electrolyte from the electrode chamber during the step of passing an electrical current through the electrolyte.
In one detailed embodiment, the method includes flowing additional electrolyte into the bottom of the electrode chamber and overflowing electrolyte from the top of the electrode chamber.
In accordance with one embodiment, the method includes bounding the electrode chamber with an electrode, disposing the article in the center of the chamber; flowing electrolyte through the bottom of the electrode chamber and flowing electrolyte upwardly with a circumferentially directed component of velocity about the article to block the formation of current induced variations in the concentration of the electrolyte.
In accordance with one detailed embodiment, the article is a tubing and the anode chamber has a cylindrical wall.
A primary feature of the present invention is an electrochemical cell having a first electrode which extends about at least a portion of an electrode chamber. Another feature is a second electrode which is the article being processed. The second electrode is disposed inwardly of the first electrode leaving an electrolyte passage therebetween. In one embodiment, the electrolyte passage is in flow communication with a conduit for supplying electrolyte and removing electrolyte under operative conditions. In one detailed embodiment, a feature is the supply conduit which has a diffusion region and a swirler disposed upstream of the electrode chamber.
A primary advantage of the present invention is the efficiency of the process which results from using dedicated cells having small volumes of fluid for repetitively performing a plating operation. Another advantage is the ability to use such cells in a relatively small area compared to large plating baths, with the small area enabling locating the array of cells adjacent to the area for the next operation on the article, such as having a plating apparatus in close proximity to an area which performs brazing. Another advantage is the quality of the coating which results from the method of flowing electrolyte through the coating apparatus to reduce current induced variations in electrolyte concentration. In one embodiment, an advantage is the quality of the coating which results from disposing an electrode about the article at a uniform distance from the surface of the article receiving a coating. Another advantage is the quality of the coating which results from disposing the coated article within the electrode and avoiding structure between the article and the first electrode. In one embodiment, an advantage is the avoidance of short-circuits as the article is inserted into the electrode chamber which results from using a guide member to position the article in the electrode chamber, the guide member not interfering with the passage of electrical current between the first and second electrodes.
The foregoing features and advantages of the present invention will become more apparent in light of the following detailed description of the best mode for carrying out the invention and accompanying drawings.